Respirators commonly include a mask body and one or more filter cartridges that are attached to the mask body. In use, air is drawn through the filter cartridge by a negative pressure generated by the wearer during an inhalation. The ambient air passes through the filter medium to enter the mask body interior where the filtered air is then safely inhaled by the wearer.
Many techniques have been used in the respirator art to attach filter elements to respirators. A common technique has the filter element disposed in a threaded cartridge that is attached to a corresponding threaded fitting on the body of the respirator; see, for example, U.S. Pat. Nos. 5,222,488, 5,063,926, 5,036,844, 5,022,901, 4,548,626, and 4,422,861. Known filter cartridges typically possess helical or advancing spiral threads that mate with a tapped collar or socket that receives the threaded portion of the filter cartridge. Rotating the filter cartridge in an appropriate direction allows the cartridge to be attached to or removed from the respirator.
In lieu of threads, a bayonet type closure has been used to attach a filter cartridge to a respirator—see, for example, U.S. Pat. Nos. 5,062,421, 4,934,361, and 4,850,346. The bayonet type closure disclosed in the '421 patent has locking tabs and notches to secure the components together. In the '361 and '346 patents, an audible device is used to indicate that the filter cartridge is properly coupled to the respirator face piece. A lug on the face piece is provided with a detent ramp or cam having an inclined surface that is positioned to gradually deflect or deform a rib on the cartridge. As the cartridge and face piece are rotated relative to each other into a locking position, the cam engages the rib and causes the rib and lug to deflect until the rib abruptly drops off the end of the cam to produce the audible click.
Snap-in engagements have been developed where the filter cartridge is manually pressed against the mask body without rotational movement to cause an audible engagement—see U.S Pat. No. Re. 39,493 to Yuschak et al. By manually pulling on the cartridge in the opposite direction, disengagement can be achieved.
In addition to threads, bayonets, and snap-fits, a variety of other connections have been developed over the years. In U.S. Pat. No. 5,148,803, for example, a bellows is used to fasten a filter to the respirator. The bellows, together with a rigid band, form a rigid cuff that receives the filter. U.S. Pat. Nos. 5,033,465 and 5,078,132 disclose the use of edge seals to secure a filter element to an elastomeric face piece. In U.S. Pat. No. 4,856,508, a foam mask shell is disclosed for receiving a filter cartridge. The foam mask shell possesses a collar that defines an opening for receiving the filter cartridge. In U.S. Pat. No. 4,790,306, insert molding is used to permanently secure a bonded absorbent filter element to a respirator face piece. A plug-in frame is described in U.S. Pat. No. 4,771,771 to secure a filter cartridge in a chamber of the respirator. The filter cartridge can be fitted to the respirator by sliding it through an opening in the plug-in frame. In U.S. Pat. No. 4,630,604, locking tongues are employed on a filter retainer to hold a replaceable filter member in an abutting relationship to the respirator frame. The filter member can be replaced by snapping off the filter retaining member from the frame. A further technique is disclosed in U.S. Pat. No. 4,562,837 where the respirator is provided with a guide ring for engaging a filter housing. The guide ring is carried by a sleeve portion that defines an opening through which the gasses pass. The filter housing slides on the guide ring from a retracted stand-by position to an extended use position.
Although the above-discussed respirators use various techniques for securing a filter and filter cartridges to respirators, these techniques have some drawbacks. For example, the filter cartridges that are threaded to the respirator typically require multiple turns to attach the cartridge to the mask body. The cylindrical geometry typically requires using the filter cartridge as an external appendage that can interfere with a wearer's vision. In other constructions, the filter cartridges may be attached with little or no rotational movement, but these devices nonetheless may project somewhat from the mask body surface. The further that a filter cartridge resides from the mask body, the greater the moment is, and thus more gravitational torque may be placed on the wearer's neck. In known respirators, the attachment commonly occurs on the inward major face of the filter cartridge, which often requires that the two parts be spaced from each other somewhat to allow for the engagement of the two parts. A final drawback to conventional designs is that a distinguishing appearance exhibiting modern appeal is sometimes lacking.